add InspectImage

[donhcd]

ping @aluzzardi @vieux @ehazlett

simple testing code:

package main

import (
        "fmt"
        "github.com/samalba/dockerclient"
)

func main() {
        docker, err := dockerclient.NewDockerClient("unix:///var/run/docker.sock", nil)
        if err != nil {
                panic(err)
        }
        im, err := docker.InspectImage("busybox:latest")
        if err != nil {
                panic(err)
        }
        fmt.Println(im)
}

[ehazlett]

LGTM

[aluzzardi]

LGTM